Many international longhaul (TATL and TPAC) fares are cheaper exCanada than exUSA, so going from Canada with a separate ticket or by driving can be a way to save money on many itineraries even though it's a big hassle.

Has OP checked for cheap PS fares to Europe using the DTW-AMS flight with a PS cabin? I've noticed some nice PS fares on certain routes that do require the one week or Saturday stay but don't have such an advanced purchase requirement? OP doesn't state the routing or cabin class he/she is planning to purchase, but PS fares can sometimes be cheaper than coach. OTOH the big savings due to routing from Canada are associated with business class since those fares are so much higher to start, so that saving some fraction becomes a lot more money.

However, if OP will fly to Canada, why consider only YWG? There might be other airports that would avoid the need to route through MSP a second time, for example FAR-MSP-Toronto and then Toronto-DTW-AMS/CDG-CPH.