You should not dump BA as a major carrier in your plans [and you've said you will want to keep your ExecClub Silver status, as long as you don't mind doing your longhauls via LHR. BA's fares ex-CDG will be very competitive even in their mid and premium cabins, so if your centralized TA is looking for good prices, BA could actually be a realistic choice. While AF will be more convenient with non-stops, its fares will be higher ex-CDG. [The irony of this is that flying AF from any other European country but France and connecting at CDG has provided among the cheapest fares for longhaul travel. BUt starting in France bumps the fares up considerably. Same holds for BA ex-LHR or LH ex-FRA/MUC. However, start your trip outside the home country of these two carriers, and the fare drops significantly.] So this should assist in keeping your BA status. Aside from short intra-European trips which will likely be more practical taking AF non-stops, you shouldn't have to make a major change in FF program strategies.

As for your credit cards, I know RBC is active in the UK, and even think they operate a version of BA's affinity Visa, so that may not pose a problem transferring it to the UK version [though that one may not contain as generous a set of benefits, including that second ticket you mentioned]. And you can likely keep the CIBC AeroGold going as long as you maintain a Canadian address for the account, and just leave it as is. Davistev has lots of experience in this regard, having lived, it seems, everywhere but Canada, so heed his counsel!