I think it's important to understand what's going on. Browsers have dropped default-enabled support for Flash, which means that users may have to enable Flash content before it will run rather than it running automatically. At some point, that will turn into a "you cannot run this at all" as Adobe has announced they're going to stop supporting Flash by the end of 2020. So, it's not as much of an issue of "Canvas doesn't play well" as much as "Nothing is going to play well".
But, yes, there are tools for creating HTML5 interactions and recent versions of Captivate can create them, so one possibility may be to upgrade to a newer version of Captivate.
I've got a problem with converting really old Captivate animations. We had the .cp files, which came along in version 4 and was created back in 2010 and it hasn't been updated since. The new versions of Captivate won't open the .cp file any more and when I download a version that will open it, it was pretty hosed and was going to require a lot of effort to fix. I've got some custom Flash that I wrote back in 2006 with Action Script 2 that becomes useless in Action Script 3. All that is to say that depending on the version of Captivate you are using, the upgrade may not be smooth and may want to consider alternatives.
You could also use this opportunity to evaluate what it is that you're really after in your interactions. Sometimes we do something because that's what our previous system allowed us to do, but it wasn't really what we wanted.
First, welcome to Canvas and welcome to the Canvas Community!
Below is some extracurricular reading so to speak...................
And finally, an HTML-5 resource: HTML5-Based Interactive Instructional Content | Site Title
As email@example.com, "You could also use this opportunity to evaluate what it is that you're really after in your interactions." The real question is always, how can I best deliver my curriculum using the tools that are available? Although I do understand not wanting to recreate already-developed content. You might also want to participate in the Instructional Designers group in this community. Lots of Articulate and Captivate users in that space; and not surprisingly, HTML-5.
I hope this helps,