With vanilla scented flowers its more likely to be Clematis armandii - there is a variety with pinkish flowers called 'Apple Blossom' and a white one called 'Snowdrift', or just the basic C. armandii. Its evergreen, with rather long, dark green leathery leaves - but it does get raher large, as its a species clematis. Flowers very early.
C. montana grandiflora is said to be sweetly scented, not sure about vanilla scented, just sweet, isn't evergreen, and flowers later, around May June time.

Yep, I'd agree with Bamboo, it sounds more like C. armandii, which is considerably more strongly fragrant than any form of C. montana, although it has 5 petals rather than 4....