回复：父母签证

1. US visa Entry is M for multi. I don't think your parent get M visa (non degree student)

2. visit canada no problem as long as they can get canadian visitor visa. they can get either in China or in US. i know several get in US the same day.

3. short time visit canada back to US no problem at all. just show the passport / I94 and will let in. most time even not get off the car and get a sign of go by the border officer.