The EU and Canada concluded an Open Skies agreement in 2009 so I presume that AC can operate any services between points in the EU that they wish to and that therefore tickets will be available on the AMS-LHR-AMS and LHR-AMS-LHR sectors.
However, with such a small aircraft, they won't have so many seats to fill (and they have no codeshare partners between LHR and AMS so they may be able to sell a good few tickets to their own passengers coming through from Canada) so it may not end up being as cheap an option as other similar tags in the past (UA used to park aircraft overnight in BRU rather than have them sitting overnight in LHR where the costs are far more expensive, and tickets on these tags were more about minimising cost while maximising access at LHR, so they could afford to almost give tickets away on the short tag.)