"While I understand the historical significance of this July 1st, I am struggling to find meaningful ways to explain it to my three young children."

I don't understand why you feel it necessary to explain anything. July 1st is Canada's 150th birthday. Kids understand birthdays. Leave the explaining at that. Drop the phrase "Canadian values". I'm a 5th generation Canadian and a baby boomer and I don't know what Canadian values are (other than universal healthcare, which isn't a value but all Canadians value it). 

The way to learn about Canada is to live here. Your kids will help Canada evolve. This Country isn't a static thing. And it's not the same from one region to another. Young Canadians should be encouraged to learn about their county. Visit the provinces and cities.. And for God's sake, teach them how to properly pronounce Newfoundland. If they can't do that then they're not good ambassadors for the Country.