On butterfly milkweed.
These are tiny—I'm guessing perhaps 6mm body length. There were quite a few of them flying around very close to the sandy ground, and periodically one would land as seen in these photos. Until I looked at them through my camera lens I thought they were small flies.
Caught by sweeping Centauraea nigra under powerlines. Tentative ID based on: https://scholar.valpo.edu/tgle/vol52/iss1/6/
@matthias22 I wonder if this is a new record for Quebec. Thanks for your insights!