Keep in mind that even though you'd be in the U.S. when you used the services, they still have a Canadian address for you, so you will be charged the cost (including the embedded GST) that you'd pay if you were in Canada. That is to say, if there are discounts for something for the person beside you with an American address, they might not apply to you. I can't speak for all things, as I only have a Kindle account with the .com site, but I have found (and confirmed with the company) that a book on sale for Americans isn't always offered at the sale price to me because of my Canadian address. Also, the price I'm offered, even though it's in USD on a US site changes almost daily, as the exchange changes. When you work out the price, it's within pennies of buying it from .ca, including the GST. Also, I can only have my account hooked up to one of the US or the Cdn site. If I buy books on the .com site, I can't use the same account to also buy on the .ca site unless I change my country designation. I can do that, but have to change it back if I want to buy on the US site again. This might also be the policy for prime and the features you're hoping to use, but I don't know for sure.We currently have Amazon Prime for Amazon.ca (which made great sense when the Amazon Visa was offered (still slightly disappointed that they stopped offering it.) Since we have a fire stick, kindle, we use the prime video, 2 day shipping rocks, etc.. it provides value for us and I can see us continuing with it as along as it provides value for us (it won't for everyone --- but does for us.)
I was looking at Amazon.com and was thinking we may do a trial membership/monthly membership for 1 month --- shortly before our trip time so we can use the services while we're there (I'm thinking Amazon Now, Amazon Fresh, video, etc... while we're there for 2 weeks.) Ultimately it would be nice if they offered a discount for international members who maintain a membership with their home country Amazon (since most of the shipping/video benefits don't work for international members unless they're shipping/situated in the US) but I'm thinking that is not likely to happen. But it might be worth it to try on our Amazon.com account (which we set up before amazon.ca was an option.)
So, long story short, you might want to send Amazon.com an email and ask about what you can get and keep on your account. It might be worthwhile setting up a new account, if you have to redirect yours to take advantage of Amazon.com prime.
Keep in mind that even though you'd be in the U.S. when you used the services, they still have a Canadian address for you, so you will be charged the cost (including the embedded GST) that you'd pay if you were in Canada. That is to say, if there are discounts for something for the person beside you with an American address, they might not apply to you. I can't speak for all things, as I only have a Kindle account with the .com site, but I have found (and confirmed with the company) that a book on sale for Americans isn't always offered at the sale price to me because of my Canadian address. Also, the price I'm offered, even though it's in USD on a US site changes almost daily, as the exchange changes. When you work out the price, it's within pennies of buying it from .ca, including the GST. Also, I can only have my account hooked up to one of the US or the Cdn site. If I buy books on the .com site, I can't use the same account to also buy on the .ca site unless I change my country designation. I can do that, but have to change it back if I want to buy on the US site again. This might also be the policy for prime and the features you're hoping to use, but I don't know for sure.
So, long story short, you might want to send Amazon.com an email and ask about what you can get and keep on your account. It might be worthwhile setting up a new account, if you have to redirect yours to take advantage of Amazon.com prime.