Since the introduction of global shipping lanes, the European green crab (Carcinus maenas) has become a highly successful invasive species, colonizing every continent except for Antarctica. First sighted in San Francisco Bay, CA in 1989, the invasive green crab population quickly spread to Vancouver Island, BC in less than 10 years. Upon introduction, a comparatively high tolerance to fluctuations in temperature and salinity allows C. maenas to outcompete native crustacean species for habitats and resources. Given that nearly 30% of the Canadian Pacific Coastline is considered marine protected area, harbouring critical native species and habitats, understating the factors influencing the survival and spread of C. maenas may be vital in mitigating their harm. Additionally, the estuarine coastline of Vancouver Island offers a highly variable environment, with salinity ranging anywhere from full strength sea water, to dilute freshwater inputs. Here, using a multi-stressor approach, we evaluated the upper thermal tolerance of the green crab in combination with variable salinity. In particular, we investigated how changes in environmental salinity influenced the critical thermal maximum (CTmax) of the green crab. First, six male crabs were assigned to each of the following treatment groups, 100% salinity, 50% salinity, 20% salinity, and acute 0% salinity, then CTmax was assessed. Interestingly, no significant differences in CTmax were found in response to changes in environmental salinity, exhibiting a CTmax of approximately 37.6 ± 0.3 °C. In response to changes in salinity, heart rate, temperature induced maximum metabolic rate, resting metabolic, and freshwater LT50 are also evaluated at various temperatures. This research offers valuable information regarding C. maenas’ tolerance to environmental stress related to variable estuarine environments, which may play a vital role in predicting and thus mitigating their invasive success on the Canadian Pacific Coastline.