Two options to consider:
1. DCF (direct consular filing) spousal visa, this might work if you have a job offer in the US. DCF is up to the US Consulate, Montreal at their discretion. It's much faster than the regular route (a few months typically), and begins by contacting Montreal with evidence of the US job offer for the US citizen. If they accept, the I-130 petition would go directly to Montreal for consular processing.
2. Regular spousal visa. If DCF does not work, you begin by filing an I-130 petition with USCIS as the first step. This can be done online. The process from filing the petition to a visa interview in Montreal will take 1-2 years.
Either way, you can continue to live together in Canada while waiting for the process, at least until a few months before the visa interview, when you will need to show that you have established domicile in the US. Montreal is very strict on this requirement. Most US citizen spouses move to the US a few months before the anticipated visa interview for their Canadian spouse, to get a job and establish a residence in the US.
Good luck!