Well I started with Duolingo. Luckily by the time I realized I can get extra points with French for Express Entry, I was already at level B2. It is not difficult to read and answer the multiple choice questions, and I can deal with the listening too. Challenge is with the speaking and writing of course. For the required level of French(It is B1 isn'it it, please let me know if I am wrong), being able to write simple sentences (for me especially the question phrases) and explain simple stuff is enough. I think if I put 1 month of full time study in it, I could get the required result. So if you have time start with Duolingo, if not you gotta work. Common sense right