I would think that if it’s from LGW it will be the Dreamliner so that will Vancouver & Calgary, the max will likely do Dublin/BFS to Hamilton, really no point in using max from LGW to eastern seaboard it just too tight on fuel westbound.
No direct from LGW to Vancouver and a 789 to Calgary -V- a Westjet 767 ? plus European feed
I think there could be a market to SWF from LGW with preclearance at SNN and direct on the return.