It has often (but not always) been my experience that you can combine the two tickets onto a single ticket, thus making the airline responsible for insuring your connections. The YVR-SEA-YVR may through a wrench into the system. But I have done DFW-TUL-DFW-RDU-DFW-TUL-DFW (to take advantage ot the Southwest effect in Tulsa) and it priced identically with buying 2 tickets (DFW-TUL-DFW and TUL-DFW-RDU-DFW-TUL.)

If you are going to use seperate tickets and especially if you use different carriers, you must allow sufficient time to insure the connection. Having a backup plan doesn't hurt either.