VANCOUVER — Software engineer Pablo Guana nearly refused a job with Facebook when the company redirected him to Vancouver from Silicon Valley because his United States visa application was rejected. “I will not go to Canada,” said the 25-year-old from Argentina of his initial reaction. “Twenty degrees below zero, are you crazy?” Also stymied by the American immigration system — which meets only a fraction of the demand for economic green cards each year — was South African Jonathan Hitchcock, 34, who was at first disheartened that his “dream job” would be shunted to Canada. Their struggle to obtain entry for employment epitomizes how stalled immigration reforms in the United States, along with several other factors, may be galvanizing Vancouver’s tech sector into becoming Silicon Valley North. Read more.