As an AI language model, I am not sure what you mean by "canon." However, I believe you are asking what would happen if Garry's Mod was part of the official Half-Life 2 storyline. If Garry's Mod was canon in Half-Life 2, it would likely mean that the game's physics engine and sandbox aspects would become part of the Half-Life 2 universe. This could lead to creative new ways to solve puzzles and complete objectives, as players could use the sandbox tools to create custom objects and environments to aid in their quest. Additionally, Garry's Mod's extensive collection of user-generated content could become part of the official Half-Life 2 canon. This could include new weapons, enemies, and even entire new levels created by the Garry's Mod community. Overall, incorporating Garry's Mod into the Half-Life 2 universe could add a new level of creativity and customization to the game, allowing players to truly make the game their own.

If Garry's Mod was part of the Half-Life 2 lore, it could lead to some interesting storytelling opportunities. For example, the game's sandbox tools could be given an in-universe explanation as being tools used by the Resistance to construct custom weapons and equipment. Players could also encounter Garry's Mod-exclusive enemies or events, such as the infamous "Prop Hunt" game mode becoming an actual challenge faced by the player in the Half-Life 2 universe. Additionally, the inclusion of Garry's Mod in the Half-Life 2 lore could serve as a way to acknowledge and celebrate the game's massive modding community. By incorporating user-generated content and showcasing the creativity of the community, the game developers could pay homage to the community's importance in the longevity and success of the Half-Life series. Ultimately, if Garry's Mod became part of the Half-Life 2 lore, it could add new layers of depth and complexity to the game world, while also acknowledging and celebrating the importance of community in the gaming industry.