Emergency crews were called to the polling station near Burnhamthorpe East and Tomken Road just before 4:20 p.m. on February 22 for fire reports.
Police found the fire suspicious and said they believed Fonseca’s office had been targeted.
The investigator said late Monday that they had made an arrest in connection with the case.
Police said 31-year-old Adam Degrassi from Mississauga was charged with arson, burglary and burglary and three counts of disorderly conduct.
He was released on bail and is due to appear in court in Brampton on June 28.
The investigators said they continue to appeal to anyone who may have surveillance plans from the area before or during the incident.
No injuries were reported in connection with the fire.
Fonseca has been representing Mississauga East-Cooksville since 2015.