Generally you have to take the "Additional Basic Qualifications" course to add a division to your certificate - i.e. if you do Junior/Intermediate, you would have to take the ABQ for Senior to qualify to teach upper-grade high school. You essentially have two choices here:
1. Take four French university courses, which will mean you won't be able to apply to a B.Ed. program until you've finished them. Then apply to the Intermediate/Senior program.
2. Apply to the Junior/Intermediate program with English as your teachable. Once you've graduated, take the FLS Part 1 AQ course. You MAY even be able to take a course within your B.Ed. program which will certify you in French. This was not very well documented but was possible when I went to teacher's college at UofO! When you've finished FLS Part 1 (which is only a few months), take the Senior ABQ with French as your second teachable.
With either option it's going to take a little while to get your Senior qualifications, but I think #2
might be better because you can apply to the supply lists once you've graduated. You can work and take your AQ courses at the same time. You may even be able to get a letter of permission so that you can work on the high school supply lists before you complete FLS Part 1. Also, you then end up being certified for three divisions, from grade 4 to the end of high school, which opens up that many more doors!