Kirkland Lake

Answer
Kapuskasing is one of the first three destinations, and Timmins is one of the last three. (Clue 1)
Since Joelle traveled directly from Kapuskasing to Timmins (Clue 3),
Kapuskasing must be the 3rd city visited and Timmins the 4th.
Hearst immediately preceded Kapuskasing (Clue 2), making it the 2nd destination.
Matachewan immediately followed Iroquois Falls (Clue 2).
Therefore, Matachewan cannot be the 1st or 5th city visited, since Iroquois Falls cannot be the 4th city.
Matachewan must therefore be the 6th destination, Iroquois Falls the 5th, and Kirkland Lake the 1st.
Final order:
Kirkland Lake
Hearst
Kapuskasing
Timmins
Iroquois Falls
Matachewan