Yes, citizens of the USA are visa-exempt . . . you do not apply in advance of travel for a temporary visa to visit Canada. Another example of Call Centre personnel who have no idea what they're talking about!
Visa exempt nationals undergo examination at the Canadian port of entry and, if you can convince them that you only intend to stay temporarily, they let you in. And soon as you're admitted, you are authorized to stay for up to six months. If you have a valid reason for staying longer, and you have documentation of your date of entry, you can
apply from within Canada to extend that status.
Most US citizens don't receive Visitor Records on entry . . . most don't even get documentation of their entry date. If you're sincerely coming to Canada just to visit your wife, you need to be able to demonstrate that you intend to go home again in a reasonable amount of time - as plumosa says, long before six months duration. Being authorized to stay for up to six months if they admit you is not the same thing as having the right to walk up and ask for authorization to stay for six months. If you do that, plumosa is right, they will require that you show that you have sufficient funds to support yourself and they will start off, right away, being suspicious of the connections you have in Canada that make you want to stay that long - and that can open a can of worms you don't want to get into. Normally, for a stay of a few weeks, a return-trip ticket is sufficient proof of your intent to go back and you'll have a routine entry. But anytime you present yourself when you have a spouse within Canada, you do have the risk of being harassed. It's really not something you should try to cover up - because if it comes out, then they start wondering what else you lied about. So, basically, you REALLY need to be able to demonstrate sound ties to home. This would include proof of a job you are going back to, a rental or lease agreement (or trust deed for property) where you live, etc. If you don't have those types of things and you DO have a significant relationship like a wife in Canada, they're not going to believe you intend to leave again and they could refuse you entry - or document you on a visitor record that limits the amount of time you can stay and which maybe even requires you to check with them on departure to prove you're going.
If you're really not intending to go home again, you should have your wife accompany you into Canada when you come. She needs to have with her proof of your legal marriage, as well as proof that she has applied for permanent status for you and that she has the monetary means to support you (like a letter from her employer) while you're visiting because you cannot work. With her being there, giving her word that this is a legitimate relationship and she is a willing sponsor, they would normally then document you on a visitor record that authorizes you to stay for six months, and that gives you the proof of entry that you need to apply from within Canada to extend that status if your permanent residence isn't approved by the time it's due to expire.
