Screenshot Proud papa or pathetic politician? Former Canadian Prime Minister Justin Trudeau and his pop star girlfriend, Katy Perry, filmed themselves prancing around a Montreal hardware store in their latest silly video together. Trudeau, 54, grabbed a plunger and what looked like a dish drainboard full of different items and mugged for Perry’s camera as his son Xavier Trudeau’s song “Downtown” played over the store’s speakers. The 18-year-old …