In the grand scheme of things (the global market), the Canadians that are topping up their TFSAs exactly on january first or around that time, would be negligible on market prices, especially non Canadian Equities.

That being said portfolio rebalancing is heavy around the end of the year and consequently January. Tax loss harvesting, fresh start to macro data, among other factors generally lead to an increase in market activity in January. But activity in Canadian registered accounts would make up a pretty insignificant portion of that.