It will install, no problem. I currently have accounts on the Canadian, US and Italian iTunes Stores, all synching apps to my girlfriend's iPod Touch.
The only caveat: you'll find that to get application updates, you need to log-in to each store and manually check for updates. Often the "updates available" counts will make zero sense. And if you have a LOT of apps, it gets pretty annoying after awhile...
Personally, I only use the US App Store. In part because I had an account from when I lived there, and in part because the number of "not available in the US store" apps I might run across is ... well, kinda low ...
(ditto for movie rentals, but not for music/audio)
It is a bit annoying to be constantly typing in different passwords when different apps need to be updated, but otherwise it's a perfectly suitable situation. I used my US account to grab the kindle app... too bad Canadians can't buy kindle books...
You can buy a kindle book. Setup a US amazon account with any mailing address. Purchase a emailed giftcard with a canadian credit card. Email that gift card to yourself and apply it to your US amazon account. You can now purchase any book you want as long as you keep your account topped up with gift cards.
They'll install and run fine, but in my own experience, I found that I had a little bit of trouble once I had a mix of paid apps from both the CDN and US stores on my phone. I couldn't get the "updates" notification to work anymore. However, once I removed the paid CDN apps from the phone, everything worked fine.
Having said that, this topic came up in an earlier thread and another poster (sorry can't remember who) indicated that he was able to update both without any trouble.
Worth noting that apps from the US store aren't taxed at point of sale. The Canadian ones are (which is why CDN ones can only be bought via credit card, whereas the US ones can be credited directly from a gift card without having to keep a credit card number on file).
{edit} I just noticed now that CubaMark has encountered the same issue.
Really, all you have to do is sign in to the US account to get updates for apps you obtained there, and sign in to the Canadian account to get updates for those apps. I do this all the time, and it works very smoothly.
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