If we want an AC ticket - discounted business class-from Canada to Delhi via Dubai- with a stopover in 1 direction. Can we book AC in one direction between Canada and Delhi (YOW for me, YVR for my sister) and then other direction book Dubai - Delhi on EF and then AC YVR/YOW - Dubai. We would want a stopover of a few days in Dubai.

I would hope that it not that much more expensive than going to AC directly between Canada and Delhi in both directions.
I would hope that is not that much more expensive than going on EK ticket (does EK codeshare on YOW-YYZ/YUL or YVR- YYZ/YUL or YVR-Dubai) whereby one can go on above itinerary.

(PS-does one have EK J class lounge access in Dubai if flying J class on AC from Dubai to Canada?).

I would hope tht is not that much more expensive than the above itinerary being a pure AC/AI ticket- ie Dubai-Delhi leg being on AI.

PS-one disadvantage of booking EF leg- we will get SDM/SQD only on AC segments but not on EK segment. Will we even get Aeroplan (non status) miles on the EK flight?