I recently travelled EDI-YUL-YSJ EDI- YUL was KLM and YUL - YSJ was AC on seperate tickets
normally only the baggage could be routed right through and I had to check with AC in Montreal, but this time I was able to have all the boarding passes in EDI, so as all your flights are KLM/NW I assume they should be able to check you right through, I would certainly show both tickets and ask if it is possible