Personally, I think it's best to start off with something small. Let's say 2 members happen to be going to a convention, meet up, and spend some time prowling the con together with some shameless self advertising (if people ask)
From there, the more frequent people see members in costume and what they're up to, we can slowly start digging into the bigger aspects like workshops/community involvement.
It's rare to see someone in Spartan gear in Canada, so it's definitely a treat if we can manage a gathering with at least 2 people.
Finances and logistical purposes, as you mentioned SPARTAN II, is a huge factor. I know for a fact that it's cheaper to do cons in Canada rather than crossing the border. Some (American) friends and I are planning to attend DragonCon next year. It'll cost me more than them for travel alone.
As for your question about charities/fundraisers; it can be up to the sole individual or as a group. I have no experience in that area either, but there was a post through social media about a 405th member who attended his annual cancer run for the cure in Spartan armor. We could do something that simple as long as the fundraiser/charity personnel are ok with it. I got inspired to try and meet next year's deadline for the cancer run. Some places may not allow helmets, but there wouldn't be an issue as long as weapon props aren't present.
Even children's charities would work. Most kids would recognize spartans before adults.
That's where my head's been as of late ^_^