I this case, I think 我明天不能参加美术课 works too, if a bit awkward.
Would this be correct?"我不能上明天的美术课"
It has the same meaning but is syntactically different. That would be more like "I can't attend tomorrow's art class"
我明天不能参加美术课? would this be okay? Could someone native or fluent confirm?
參加 is more like participate than attend
可以这么说,没问题。
what about 可以 instead of 能?
Use 可以 if you the situation is you are not accepted to the class or something is preventing you to attend your class
Is it incorrect or awkward to use 来 or 回 instead of 上 here? Neither is accepted.