I just moved to the US & I need to mail something out to Canada, but I don't want to send it out for another 2 months. Can I buy the stamps in advance if I want "Express" stamps if there is such a thing?
I want it to arrive like 3 days after mailing it out.
The reason I ask is cause in Canada where I used to live, if you wanted to send anything express, you have to get the stamps and process it at the post office the day you decide to mail it, and you can't do it way in advance. Is it the same in the US? anyone know?

It is the same way here. They don't hold mail.
Go to the United States Postal Service website. www.usps.com for more info and rates.

no you can't buy "express" stamps in advance .
there are numerous ways to send a letter/package in 3 days........
from the US post office you can express or priority mail, you can use FedEx, or UPS or a similar shipping company.

any route you decide to take will require you dealing with it at the time you actually want to send the letter/package.