The area, in the San Lucas mountains, is a traditional ELN stronghold.
A regional security official, Jose Hilario Bossio, told the AP that the kidnapped men included engineers and geologists. He said soldiers and police were searching the sparsely populated area in the San Lucas mountains. The armed forces said it had put planes in the air to try to find them.
Canada's Ministry of Foreign Affairs said it was aware of the reported kidnapping of a Canadian in Colombia but provided no information on his identity.
The two Peruvians were identified as Javier Leandro Ochoa and Jose Antonio Mamani by Peru's consul in Colombia, Jorge Davila. It was not immediately clear if they were Braeval employees.
The chief of Colombia's anti-kidnapping police, Humberto Guatibonza, said he was aware of two other foreigners being held by kidnappers. He said one was from the Dominican Republic and the other from Guatemala and both were taken by common criminals rather than by illegal armed groups.
Colombia's vice president, Angelino Garzon, appealed to the ELN to immediately free the five prospectors without condition.
Associated Press writers Frank Bajak in Lima, Peru, and Charmaine Noronha in Toronto contributed to this report.