I saw this on the BA website:
https://www.britishairways.com/trave...club/_gf/en_us
Travelling in more than one cabinIf you are travelling in more than one cabin, e.g. outbound in economy and return in business class, you will be given the more generous allowance for the whole journey.
Travelling with separate ticketsIf you are travelling on separate tickets, the baggage allowance for each ticket will apply individually
Based on the first statement, I would think that we are OK with 3 checked bags per person on the out bound segment even with a seperately purchased CE ticket to CDG as long as we can link the YVR-LHR segment with the LHR-CDG segment since our return (CDG-LHR-YVR) is ticketed in F.
Comments to the contrary are welcome in order to prepare.
Linking does not mean you no longer have separate tickets. Hopefully they will just check them through on the outbound and ignore that there are separate tickets -- but be prepared to have the baggage allowance calculated separately according to the rules.