without doing a bunch of legal research, i think not. you could go get a marriage license, get married. that should dissolve the civil union as the marriage is of greater status than the civil union.
i doubt that there is any law on this. the civil union statute says nothing about this.
the marriage act says a prohibited marriage is one in which either party is married to someone else and that marriage is not dissolved. a civil union is not a marriage.
based on a quick reading of the statutes, i say go for it.