You don't lose any rights as an American citizen, if you go up there...What are you talking about?
First off, the Canadians, have atleast as many rights as the Americans do, maybe more, and they're a lot more respectable, and humble about it, too. They don't go bragging to the world, and boasting about it to everyone, but in reality, they've got more freedoms than we do, and just about as many rights, with the exchange of a few. So big deal, they gave up their guns, they've got the med coverage instead which is likely more valuable anyways. I hate all of this American crap I hear all the time about us being the freeest country in the world and all of that... because its B.S. How many of you guys, out in Australia, or up in Canada will back me up on this one? I'm an American, but that doesn't mean I am free, or have free rights these days.
Second off..In moving to Montreal for work, he will not need to renounce his US citizenship or anything like that. Same as being here on a work Visa, they have a nice program for that over there. So, He won't be losing if he takes the job.
Finally, If being paid, in US denomination, and living in Canada...You've got it made. Our dollars go further there to begin with, and they love American money.