As far as I know, all playoff games are available nationally in Canada via Sportsnet and CBC with no blackouts. For the playoffs in Canada, you need only a cable subscription that includes Sportsnet, SN360, CBC or a subscription to the Sportsnet+ app which provides the games that air on those channels.
The one Montreal game so far in these playoffs aired on both CBC and Sportsnet as does the second game tonight. So, there is no reason your father should have blacked out.
If you are referring to him being blacked out of a regular season game, then yes, if he lives west of the Belleville-Pembroke line, he is outside the Montreal TV terrirory and any games on TSN or RDS (french) would be blacked out. He would only get games on SN/360 or TVA Sports (french). Any games that are part of the Monday night Amazon Prime package would only be available to him via Amazon Prime Video. But once again, this is only in the regular season; it does not apply to the playoffs.
There are no regional broadcasts in Canada during the playoffs. There are no games broadcast anywehere other than Sportsnet/CBC and those games are all available nationally. So, blackouts do not come into play during the playoffs in Canada.