Hi,
Welcome to the forum.

I think you may not be fully appreciating how QU works with image and print resolutions, see http://www.ddisoftware.com/qimage-u/tech-prt.htm for full details.
However, in summary, QU always interpolates the image and sends the data to the printer at the printers native resolution which for Canon is 600ppi when the driver is set for best quality. The algorithm used (Fusion) is far more advanced that anything else available.
This is the fundamental principal of how QU works to get highest possible quality prints. You do not have to be too concerned about what the numbers are, QU looks after it for you. Do not resize the image in any other program, merely use the original image, specify the print size and QU does the rest.

Where are you reading this ppi data and are you referring to Page size or Print size, they are not necessarily the same?
What you see in the Print Queue tab is the print size divided by the image pixel size, see 1st screen shot below.
What QU is interpolating too is shown above the page preview on the main screen, see 2nd screen shot below.
This is what QU reports from the driver so make sure your driver is set to get the highest quality and set from within QU so it is remembered.
Terry

Hi, and as Terry said, Welcome!

Trying to help, so we need to understand ....
We need terms like page size and print size. (Custom size media could be either)

In Job properties, we see MAX ppi. That reflects your setting in the print driver.
That should say Max 600 on your Canon unless you change something in the driver.

The other screen snap attached is the Print ppi. This one is totally dependent on print size and image resolution.

So it would help if you would fill in where you are confused.

Thanks,
Fred
PS Terry is washing his car, and it needs it badly.

The only way those native resolution numbers change is when changes are made in the driver.
I dont have that driver to look, but what is the maximum width of a page.
I see 60 x120 and 60 x 60 x 90
These are numbers that your driver feeds back to Qimage.
Has nothing to do with the print sizes.
It is likely that the driver will lower the native ppi it needs when the page size is too large to handle 300.
I also see that when large size prints  60 x 90 plus, even the 600 ppi is no longer offered.

So let's move on to your print side of the question.
If you made an image already in some other software which was saved at 10 x 15 @ 300 ppi, then go to Custom size in Qimage and select USU ORIGINAL SIZE
What size prints are you making from what?
How many on the page?

Fred

Exactly right.
Your Driver is changing native ppi as you increase page size to where the print file stays manageable.
Qimage is only reporting this information to you, not creating it.

 
Next question is what size prints and how many on that 60 x 120 or 60" x 90" page?

Just as an example, I placed a few (4) 11 x 14 prints on a page size of 44 x 125.
If you look at the snaps, you will see that the 11 x 14s have varying ppi. This is due to the resolution of the images presented for printing..
Some have been cropped, and some not.
This is normal and preferred. You really don't want to set a predetermined ppi unless you are sending images for printing to a lab that requires 300 for their special driver.

Hope this clears up the confusion.

Fred

Some drivers on the larger format printers automatically lower the PPI when you select a large paper size.  Epson's often change from 720 down to 360 for example.  I've never seen one drop as low as 200 but there's a first for everything.  And with most drivers, there is an option in the driver to override and use the best quality.  Example: in the Epson driver if you dig deep enough in the driver settings you'll find an option called "Finest Details" on those large format printers.  Check it, and the PPI goes back up from 360 to 720 even on large pages.  So take a careful look in the driver to see if there is any "best quality", "finest details", or some similarly worded option you can check to bring the quality back up to 300.

Regards,
Mike

And the resulting display in QU after doing the above...

In reading the Canon help on the "Fine zoom" option, you want that set to "No" when printing from QU.  Apparently "Fine Zoom" allows the driver to request lower PPI from printing software to minimize data problems from printing software packages.  That might be OK for other programs because they try to send the whole print at one time (thus using too much memory) but QU already automatically tiles the print data in small chunks so that never happens.  The result is that you can typically use maximum PPI even for a 10 foot long print when printing from QU.  So you're safe running it at 600 PPI on huge prints.  After selecting "No" for fine zoom, you can select "Standard" for the quality setting on the first screen snap if you only need 300 PPI though.  That's probably more reasonable for very large prints although with QU, I bet 600 PPI would be no problem.  It'd just take longer to print something that size.

Mike

Not only is QU merely a "poor man's RIP" for laying out & nesting prints on a page, it does what you say in the quote above automatically anyway.
Now that you own QU, you also have a business improvement opportunity to eliminate that part of the order process which "automatically upsamples/downsamples as needed" because that is what QU does and does it in a superior manner.
It seems you are hanging on to a step in the process that was required by programs such as PhotoShop to specify a print size and resolution. Miss that step out completely and specify the inch size of prints in QU (which you seem to be doing anyway) and let QU do its stuff with respect to resolution.
Terry