Because your remote Canadian workers will be living and working in Canada, they don’t need US work visas. They are considered to be Canadians working full time in Canada. 

However, if these workers need to travel into the US to work on American soil (e.g., if they need to service your domestic US clients or do actual work at your company facilities), then your company does need to get a work visa for them, even if they work mostly in Canada. Your Canadian employees can travel to the US for meetings or conferences. See "Can my Canadian worker work at our US Office".