Hi,
I successfully applied for an open work permit. The Canadian embassy stamped a TRV for 1.5 years in my passport. This TRV will be expiring in about a month. My question is: If I arrive at a Canadian port of entry several days before the expiry of my TRV, will immigration issue me a work permit for 3 years, the maximum length allowed? I understand that the TRV and the paper Work Permit are 2 separate documents, right?

The expiration of the TRV would not necessarily limit the potential validity of the work permit. The latter would be governed by whatever approval was rendered in your case.