A quick google search gave me this: https://canadianpayrollservices.com/legalities-hiring-remote-canadian-workers-us-companies/
(check this) http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=172&top=17
(and this) http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=177&top=17
(work permit might be an issue): https://www.canada.ca/en/immigration-refugees-citizenship/services/work-canada/permit/temporary/eligibility.html
Long story short, your husband will most likely be required to apply for an open work permit (not specific to an employer) and he can start work as soon as he receives it. The fourth link I mentioned says the person has to prove he/she will leave the country once work permit has expired. However the previous link says open work permit is an option. I know of a few cases when tourist visas have been rejected when PR application for same person was in process. Open work permit might be best option. Also, if you’re still in doubt, might be worthwhile to consult a lawyer.
There are two aspects to consider: 1. Legality of work 2. Taxation.
- Legality of work: w.r.t. holding the right “legal status” in Canada that allows you to work while being physically present in Canada. In general you’re not allowed to work on tourist visas, and US citizens who are allowed to travel to Canada without any visa are generally limited by the 90-day limit, and have to apply for a work permit if they want to work in Canada (https://www.visaplace.com/blog-immigration-law/canadian-work-permits/american-work-canada/).
Note that when it comes to work visas, the general understanding is that any person “working” in a country he/she is physically present in, irrespective of where he/she gets paid from, needs a respective work permit/visa that allows said work. Meetings/short term visits etc are exempt in most cases.
- Taxation: This subject, although not related to this forum, is important since you want to avoid dual taxation. There are tax treaties that your Canadian tax consultant will surely know about to avoid double taxation.
Hope this helps.