I have had non-status friends fly FC to Canada in the past and have had no problems getting SC access. In fact, I've used my miles a couple times to book a friend in FC for his occasional trips ATL<>YUL and when in FC on that route, he makes a point to stop in the SC since he usually doesn't have access.

If DL is now interpreting their website language as DL-operated, "First Class" travel from US to Canada being ineligible for access, this represents a very real change in the policies and the loss of a benefit of the premium cabin travel "experience" on those flights.

The least they could do is be a little more clear in what the new access policies are.