TarasD
Whoever told you it was closed is who you should ask for confirmation.

Chemin du Lac d'Argent is a remote rural area. By the time someone with local knowledge sees your Note ... the construction (if there is any) is likely to be finished! ;)

I don't see any road closures (or construction work) reported in that area by Google Maps or by Quebec 511.
http://www.quebec511.info/en/Diffusion/EtatReseau/Region.aspx?id=10000

