Ouch, I wouldn't fancy a LUX-PIK-SFO/SEA like today! I assume one crew would then do the likes of the SEA-SFO-YYC part and then another crew YYC-LUX?
I don't work for CLX, but some limited knowledge of the goings on through Prestwick. As far as I know, there are weekly LUX-PIK-SFO and LUX-PIK-SEA services, PIK-SFO service today, and there was a PIK-SEA on Friday. I'm not sure of any others routing out through PIK.
Some ORD, IAH and JFK flights returning to LUX route via PIK also, but not sure how regular they are.