Although I cannot independently verify the sources, I've certainly head multiple related rumours. It's highly sensitive trade information, specially for 2 publicly traded companies, you likely won't hear many people talking about it.

Apparently there's an internal memo couple months ago to senior pilots/management pilots "strongly suggested" the potential of A350 ops in the near future.
There was also a group of senior Air Canada management travelled to Toulouse in November last year, the intentions weren't publicly disclosed, they could be just finalising some details about the XLR deliveries, final configs, etc. but it could be also preliminary studies/negotiation for the A350, and the deal was closed in late April as @Nightflyer787 suggested.

We will know soon enough if it's entering service in 2027, maybe the order will be announced at the Paris Air show.