Monster Hunter Stories can be seen as canon to an extent. It expands the lore and adds new elements that are consistent with the broader Monster Hunter world, but it might not have a direct impact on the mainline game storylines.
The Hunter x Hunter manga is unfortunately not complete. The author has faced various issues that have led to intermittent breaks and an unresolved storyline.
The Hunter x Hunter manga has indeed concluded. However, the ending might have left some fans wanting more or with mixed feelings depending on their expectations.