How do you do the OLCI at T-24 on Westjet.com if you only have the Delta confirmation # ?, or are you able to select the Westjet seat at T-24 using the Delta.com OLCI?

Related question; if you checkin with Westjet for the first flight, YOW-YYZ, connecting to Delta flights, YYZ-DTW-ATL-SRQ, does the Westjet agent charge the $25 fee for checked bag on Delta's behalf or is a checked bag free as per Westjet policy?

thanks