Welcome to the community!
Unfortunately, I don't think you'll be able to keep your Fido services while you're at University in the US. While Fido does offer roaming in the US, roaming on other mobile networks is a courtesy meant on a temporary basis only. Ususally, that would mean that the majority of your usage would have to be on your home network. If you're spending the majority of your usage on US networks, those networks would rather you pay them for using their services.
I can understand wanting to keep your phone number. Unfortunately, I don't think that would be very easily accomplished. It is not possible to port a phone number to a provider in different Country. There have been discussions online as to how best park a phone number for an extended period. Some have suggested porting to a pay-as-you-go service, though you would have to top-up periodically. Others have opted for porting to an IP service. Each method would have its own pros and cons.
Not whate you wanted to hear, but hope this helps 😀