Alternative advertising is the same as guerrilla advertising.
It's unconventional and unexpected.
It can be anything from street teams, to car wraps, to
promotional exhibits, to postering blitzes. Basically, it can be
anything you want it to be. There are no limits and many agencies
create custom campaigns.
Nowadays, people like to take conventional advertising (TV,
magazine, radio, out of home, newspaper, etc) and revamp them to
create cool guerrilla marketing tactics.
Guerrilla advertising can also be called non-conventional
advertising, guerrilla advertising, ambient advertising, and viral
advertising.
check out these sites:
www.guerrillaadvertising.ca
www.mangomoose.ca