Entering the US to renew your visa doesn’t necessarily work. CBSA has final say at entry and can
- Allow you entry and grant you 6 months
- Allow you entry and grant you any time from 1 day to 6 months
- Allow you entry with the existing visa with the time left.
- Deny you entry to Canada.
It really is a risky way to try and extend or renew your visa. Entry with a TRV is never guaranteed and CBSA tends to frown on people trying this. Best bet is what was mention previously and apply for an extension.