Americans don't need visitor visas to visit Canada.
You can visit him and get married while you're there. You can then apply inland or outland. Outland tends to be faster for Americans, but inland allows you to get a work permit and work while waiting for the process to complete.
As a visitor, you will initially be able to stay in Canada for 6 months, but this can be further extended. If you apply for the work permit (if you go the inland route), the work permit will give you status as well.
How long have you been together? I see you haven't visited him, but has he visited you? It's generally not a good idea to get married during your first visit. Ideally you'd have several visits and spend a certain amount of time together in person before marrying and applying.
The other option is common law. For that you need to live together for 12 months before applying. You could come to Canada as a visitor and extend your initial 6 months to another 6 months to satisfy the 12 month requirement.
