The 42-year-old man, who lives in the Durham region east of Toronto, was arrested Thursday after allegedly making arrangements on social media to meet a 15-year-old boy for sex.
In fact, Ontario police said, the "boy" was an undercover police officer, and when the accused showed up at the meeting place, an arrest was made.
He has been charged with attempted aggravated sexual assault as well as luring a child via computer.
Police said the man is HIV positive, and it's believed he contracted the virus in the 1990s.
"The accused had an extensive social media presence, and investigators are concerned there may be further victims," the Durham Regional Police Service said in a release.
The man used the profile name "collegetoy2033" on social media sites.
He had been a church youth counsellor in Sussex, N.B., Rochester, N.Y., Amherstview, Ont. and Saskatoon.
The man has been held in custody pending a bail hearing.
Police are asking anyone with information to contact the Ontario Provincial Police's internet child exploitation unit at 1-888-579-1520 (ext. 5363) or Crime Stoppers at 1-800-222-8477 (TIPS).