Potentially a couple of things, actually. First as was posted above, lots of barren empty space for testing, as well as access to the North for forward detection if necessary (recall the DEW line designed to detect incoming Soviet bombers). Second, backup facilities like the fall-back command facility for NORAD underneath North Bay, Ontario (there's a Canuck on the command team in Cheyenne).
We're also no slouch when it comes to satellite and space technology and that may come in useful.
First as was posted above, lots of barren empty space for testing,
The US has plenty of open-spaces sites to test.
…as well as access to the North for forward detection
The US has many satellites that will give us plenty of early detection.
Second, backup facilities like the fall-back command facility for NORAD underneath North Bay, Ontario (there's a Canuck on the command team in Cheyenne).
The US can easily build it own fallback command facilities thousands of miles away and still on US soil.
We're also no slouch when it comes to satellite and space technology and that may come in useful.
Good, Canada can build it’s own defense, if perchance, they feel their new allies in France aren’t up to the job.
I know there are millions of great folks in Canada, and I am sure you are too. But in the last year there has been far too much anti-America sentiment, words and actions coming from Canada for it to be considered much of an American ally.