While I personaly oppose the introduction of real world national holidays into video games such as this as a general principle, since that ship has clearly already sailed with regard to PSO2, I feel it is only fair to extend the same courtesy to the people of other nations included in this service region that we extended to our American brothers and sisters by holding this Independence Day event.
This at least certainly includes Canada, and possibly includes countries within Central America and the Carribbean (although since there are so many, a single holiday for each sub-region may have to suffice). Thus I offer my somewhat reluctant support in the hopes that we can help make more players feel welcomed and acknowledged.
As Golbleen mentioned, this event primarily uses already existing assets. What assets could we use for other such holidays? While it's not exactly accurate to the reality of much of the Canadian geography that people actually live in, we do have a tundra tileset that we could draw from for a quest or lobby decorations.
Outfits and accessories might be more resource intensive, but something simple like a hockey player, lumberjack or voyageur outfit might be possible. The model for US flag cape accessory could easily be re-used for a Canadian flag cape, although I don't think the Canadian flag is as significant in Canadian culture as the US flag is in US culture, so maybe a different symbol would be preferred.
A bigger problem may be the proximity of Canada Day to Independence Day as the developers may not want to use such resources on an overlapping event. Are there other, similarily significant holidays in Canada that would serve as alternatives to fill out the event calender? I know that there's Victoria Day, but that might not be specific enough to Canada to qualify and might been seen as offensive to anti-monarchists.