has anyone ever got the train to Bourg, so I can bike in around Les Arcs?

I took the train to Bourg in 2011 (But in January and overnight). I’m sure you can take bikes as they have plenty of room for snow gear .

No summer train to Bourg IIRC.

The snow train stops in April but you can still get there by train. You might need to go to chambery/aix les bains/ Lyon and change though. Shouldn’t be too hard.

london to bourg well one stop from bourg for skiing, changed at paris, overall super fast comfortable enjoyable, shuttle bus was 20 mins late to les arc but no problems at all

I’ve done the overnight snow-train a couple of times: you don’t need to change at all. As above, I don’t think that runs in summer though – I think you can change onto the TGV at Lille – we did that once (winter also).

Not that easy to get to in the summer. Have a look at RailEurope for times. Geneva is easy for Morzine. Unless you want to pay the £20 each way fee for bikes on Eurostar you will still need a bike bag.