I have flown Westjet several times under DL flight numbers and they have always told me I get my DL baggage allowance - gone skiing so have checked up to 2 bags plus a ski bag with no problem..You can;t get the seats assigned ahead of time, very true no matter how hard you try, but the airport agents are usually very nice (like most Canadians are..
) and have sometimes (but not always) even given me a plus seat for my status with DL (DM).. I've always had a pleasant experience flying them, although I try to stick to DL as I usually get upgraded to F anyway on the CAN routes.. but Westjet is not bad at all.