The 29-year-old former 24 star announced her happy news via Twitter.com on Sunday (02Sep12).
She wrote, "Happily, happily, happily, happily engaged! This has been the most amazing weekend ever."
She began dating 27-year-old Phaneuf in 2008.
The couple staged a surprise engagement party for friends and family members at the New Glasgow Lobster restaurant in Prince Edward Island, Canada on Sunday night.
Cuthbert has always been a fan of ice hockey's leading men - the Canadian actress has previously dated Sean Avery and Phaneuf's Maple Leafs teammate Mike Komisarek.
She'll become the third leading lady to wed an ice hockey players in recent years - Carrie Underwood and Hilary Duff both married stars of the sport.