You *could* say that Canada was a Christian nation when it was founded (or settled). But that is essentially applying a current day context to a time in which it doesn't make sense.
Everyone involved in the founding of Canada was "Christian", or at least Anglican. The head of our Nation is the Monarchy, who ruled by divine right. Past that, the religious aspect was and still is largely traditional.
The US was founded by elites deeply influenced by the Enlightenment thinkers of France and England. A big component of the Enlightenment was the rejection of traditional authority and the rejection of anything other then "Rationalism". So, comparing the two nations at birth, Canada was an extension of a traditional Christian nation deeply entrenched in tradition while the US was founded on the rejection of the traditional English rule.
But as I said, it might be a bit misleading to call Canada a "Christian" nation at founding since it was mostly cultural and tradition rather then a deep sense of belief at the base of things like the "Lord's Prayer" in Ontario.
That's my own interpretation of it. There are other views which basically assume that because the culture was more or less Christian, it necessarily follows that Canada was founded as a "Christian Nation". History doesn't really lend itself to absolute answers in this regard.
I doubt I answered your question, but it was fun to break out the undergrad knowledge