The 21-year old, currently with the national team for a busy summer of international rugby, will meet up with his new colleagues at the Ospreys ahead of the new season.
Hassler has four Canadian caps to date and made his debut against the USA last June. He featured twice in last November's international series in Colwyn Bay, scoring two tries against Russia in north Wales.
He has also been a central figure for the national sevens team on the 2012/13 IRB Sevens Series, playing in 33 matches and touching down 13 times.He is currently part of the Canadian squad currently competing in the Pacific Nations Cup along with Fiji, Japan, Tonga and USA.
After committing to the Ospreys for 2013/14, Hassler commented: "This is a fantastic opportunity for me to play for the Ospreys, a great team that is consistently up there at the top of the PRO12. To be a part of a squad that includes so many top Welsh players, Grand Slam winners and British Lions is a really exciting prospect.
"I'm really grateful to the Ospreys for offering me this chance, I can't wait to report for training and I'm looking forward to challenging for a place in the team next season."
Andy Lloyd, Rugby Operations Manager, said that he's expecting Hassler to make a big impression at the Liberty Stadium.
"It's no secret that we've been looking to strengthen our back three options and in Jeff we believe we've found someone who can have a real impact" said Lloyd.
"He is someone who has the pace needed on the wing, but also a physicality that marks him out as an impressive young athlete who is big and strong, exactly what Steve Tandy feels we need to support the wingers we have here already. He came to our attention when he played in Colwyn Bay last year and we've tracked him closely since then.
"He's still very raw but the coaches are confident he can add something different to the exciting blend we are trying to develop in our backs. Jeff is determined to make a career for himself at the highest level and the discussions we've had with senior officials in Canadian rugby, including national sevens coach Geraint John, make it clear that we've signed an individual with the right mindset to be an Osprey.
The Ospreys have already announced the retention of 13 key players while the signing of Italian international Tito Tebaldi has also been confirmed for next season.