Eh, I see lots of bad advice on this thread.
Let me try to cut through it all with but a single bit of advice.
DO NOT RESIZE.
Either you have your own large-format printer that you'll be using or you don't.
If you do, you're not coming to the Canon Rumors forum for advice on how to use it, which means that, if you're here and reading this, then you're not the printer operator.
Resizing is a job for the printer operator. That's what you're paying for.
Just prepare the file to the best of your abilities, and let the printer operator figure out how to get the best possible output for that particular printer.
You're not only not going to do even as good a job as the seasoned pro, you're going to make things worse. Once you've done your resizing, the damage you've done to the file can't be undone.
So, just hand over the file and be done with it. If you don't like the results, discuss it with the printer operator and be ready to take your business elsewhere.