Because my landline number is unlisted, I get no spam or solicitation calls. If I switch to Sonic Fusion, will I be opening myself up to those kind of calls?
When you switch to Sonic Fusion phone service, the listing will remain in the state that it exists in at that time. In your case, since it's unlisted, it will remain unlisted.
Sonic does not have any way to change that setting once you have moved your service over. Thus, ensure that it's set the way you want it before migrating.