The 21-year-old Canadian international left-back previously trained with the Championship club last December.
The 21-year-old Canadian international left-back previously impressed Brighton boss Chris Hughton while training with the Championship club last December during the MLS offseason and is now set to begin the coming campaign with their Under-21 squad.
"We know all about Sam and his qualities from his time with us last December,” Hughton told Brighton’s official website. "He initially began with our under-21 group, but quickly showed he was capable of stepping up to train with our first team.
"He will join the under-21 squad and his challenge, along with others, is to make that step up into the first-team squad."
Whitecaps head coach Carl Robinson added to whitecapsfc.com: "We continue to look for ways for our young players to develop and this will be a great opportunity for Sam. We'll be tracking his progress closely while on loan as he remains an important member of our club."
Born in London, Adekugbe lived in England until the age of nine before moving with his family to Calgary, Canada, and going on to join the Whitecaps Residency programme in September 2011.
The two-way defender later made the step up to the MLS roster as a Homegrown player in September 2013 and has since featured 25 times for the club across all competitions, including two league appearances and two Canadian Championship starts this season.
He has also earned three caps for the senior Canadian international team after representing both the Under-18s and Under-20s, making his debut in a World Cup qualifier against Belize in August 2015.
Last December’s spell with Brighton was his third offseason training stint in the UK, having spent time with both Liverpool and Scottish giants Rangers following the 2014 MLS campaign along with Whitecaps teammate Christian Dean.