Sept 26 (Reuters) - Swedish electric car maker Polestar is nearing a deal to go public through a merger with blank-check firm Gores Guggenheim Inc (GGPI.O) at a valuation of $20 billion including debt, according to people familiar with the matter. The premium EV maker, owned by China’s Geely (GEELY.UL) and Volvo Cars, could announce its plan to go public as soon as Monday, the people said. Polestar raised $550 million in external funding in April and announced plans in June to build Polestar 3 electric sport utility vehicles at Volvo’s U.S. plant in South Carolina starting in the second half of 2022.