In terms of allophones, that is to say those who speak a third language, a large number of those who define themselves as allophones are able to speak French. I think the issue is more about determining how to include them in the definition of francophones.
Some definitions are more restrictive and others are broader in terms of who is included in the category of francophones. The same applies to defining who is anglophone. Under the most restrictive definition, a person's mother tongue must be French to be considered a francophone. This may well limit the number of francophones, since it excludes from the definition people with a third language as their mother tongue even though French is the language they speak most often at home. Consider the growing number of people with Arabic as their mother tongue and French as their second language. Are they francophones? Personally, I think so.
Depending on the definition, the picture changes. If we want a full picture, we must agree on the most inclusive definition to determine which people are considered francophones in Quebec and elsewhere. That's what Mr. Dupuis is doing: when he says 2.7 million people, he uses a broader and more inclusive definition of francophones.