So, the wait it works is that even if they are recruiting today, that doesn't mean they are still recruiting next week. So none of us can really give you any useful information about whether they are hiring for that position or not. Even if you apply today, the recruiting center isn't going to check if they are going to process your application until a couple weeks from now.
If you are just trying to get in the Canadian Forces ASAP, then yes you should definitely consider other trades. The trades you apply for, don't have to be the trades you get hired for. You shouldn't apply for something you really wouldn't accept a job in and give your best effort on, but if you apply for something and later on decide you only want Boatswain, you can always remove the other choices.
It's a long recruiting process. If you are serious about joining and think you have your life in order to do it, then just fill out the application and wait to see what the response from the virtual recruiting center is. If you just apply for Boatswain, and they aren't hiring for them when they get to your application, they will tell you to consider other choices/apply later/consider reserves. Even if you only apply for Boatswain, and they are hiring lots of Boatswains over the next 5 months, there is still no promise you can even complete your testing/interview/background checks etc by then.
Me and a bunch of other people I know are over 5 months in to the application process, and still waiting for Medical to be approved, and still have our interview to do after that. The trades we applied for are "closed" now, even though they were hiring like MAD when we first applied.
So I would just check out all the other trades that might interest you, there are lots of great Navy jobs out there if that's what interests you. If you could see yourself doing others, apply for those in addition to Boatswain. If you do more research later or find something you don't like about it, just tell the recruiters you want it removed.
