The TSB said Monday that four investigators are on the ground to examine the wreckage and said they will be documenting every car.
The National Transportation Safety Board, the TSB’s U.S. counterpart, is also part of the investigation, but TSB did not say in what role.
Thirty-two of the 104 cars on the train left the tracks on the morning of Feb. 6 just east of the community.
A dozen oil cars caught on fire and burned until early Saturday morning.
CP said crews continue to work to ensure the removal of all equipment and the site is fully restored.
The track was re-opened Friday evening after it was cleared and the line inspected, CP said.
“We also thank those impacted by the evacuation for their patience and understanding and apologize for the inconvenience this incident has caused,” CP said in a statement.
“CP will continue to work with the affected residents who have now returned to their homes.”
Just over 80 people were evacuated Thursday morning to nearby Lanigan as the fire spread thick, black smoke into the air.
They were allowed back home late Friday afternoon.
Highway 16 remains closed to traffic between the juncture of Highway 20 to the juncture of Highway 2.
Delays of 20 to 30 minutes are expected, and a detour runs from Highway 20 north to Grid 340, then south on Grid Range Road 2233.
It is the second derailment in just under two months in the same area.
Thirty-three oil tank cars and a hopper car jumped the rails west of Guernsey on Dec. 9, 2019, less than 10 kilometres away from Thursday’s derailment.
TSB said 19 oil cars lost its entire load, and 1.5 million litres of crude oil were spilled.
It became engulfed in flames and burned for approximately 24 hours.
No injuries were reported in either derailment.
Guernsey is located roughly 115 kilometres southeast of Saskatoon.