I did that before. it's like flag-poling. My experience here in Canada have been so colorful, yet i'm not loving the loooong wait for PR... but anyways, you don't need a US visa to do that. they will turn you right back around anyway and do everything in Canada border side. although, this might be risky. I've done it long time ago (2016) when I transferred from visitor to working. also, given the covid situation, borders might still be close? and trust me, they are not that 'welcoming' on the other side. bottomline is, just wait. I have a CBSA friend, he told me to wait inside Canada for PR, hence why I applied for a BOWP to maintain status.