It doesn't at all guarantee that they will pass. In our region, in northwest New Brunswick, students don't even have the option of taking the exam in English because they aren't sufficiently bilingual that it would boost their chances of passing.
I know that, last summer, two of our students wrote the exam in English and passed, but they were native anglophones, so they were comfortable in English.
We have a French program, but students have to rely on English resources to prepare for the French-language exam, which is very poorly translated. Given that it is not adapted to Canadian French, it does not take into account all of those important language distinctions. It's so bad that students tell us they don't even understand what the question is asking. They read the words but aren't sure what they are being asked. It's not at all familiar to them. What's more, they have studied the terminology in English, so it's extremely difficult for them right from the get-go. Passing isn't easy under those circumstances.