WS only files one-way non-directional fares which allow end-on-end combinations with themselves (vs. other carriers that file round-trip fares or directional fares, and/or have restrictive combination rules).

If your fare origin is YYJ, then booking one ticket will use YYJ-DUB fares (published in CAD) for both directions.

If you book two tickets, YYJ-DUB and DUB-YYJ, only YYJ-DUB will use those fares. DUB-YYJ will use DUB-YYJ fares which a) are published in EUR so you will need to convert to sales currency (i.e. CAD) and b) are different.