President Donald Trump upended relations with one of the country's closest allies and trading partners when he suggested that the US should annex Canada and threatened punishing tariffs on certain Canadian imports.The fraying relations between the two nations could also disrupt one of the biggest pipelines of money into US commercial real estate.Since 2015, Canadian investors have acquired roughly $184 billion of US multifamily apartments, office buildings, retail spaces, industrial warehouses, and other commercial property assets, according to data from MSCI. That's more than any other foreign investor.There are now...