The XL pipeline would provide only temporary jobs for the construction of the pipeline. It might require a few dozen permanent jobs for maintenance and other costs associated with any ongoing concern. Then again, the US firms (if any) charged with maintaining the pipeline once it's built may not hire anyone new for these roles.
Not quite. This is from the US state department:
"The Keystone XL project, if built, would support 42,000 jobs over its two-year construction period. The report notes that building the pipeline would support approximately 42,100 direct and indirect jobs and contribute roughly $3.4 billion to the economy (that's about 0.02 percent of GDP).
About 3,900 of those jobs would be temporary construction jobs. After two years, once built, the pipeline would support 50 jobs."
"The State Department thinks blocking the Keystone XL pipeline would have only a small impact on tar-sands production and climate change. So what happens if Keystone XL gets blocked? Here the State Department seems pretty confident that the oil will find its way to market anyway — especially by rail."
"Transporting oil by rail carries more environmental risks than by pipeline. The report adds that, if the pipeline gets blocked and producers are forced to ship by rail or truck instead, overall transportation emissions for the oil in question could even increase by 28 to 42 percent. That's because there would be more trains and trucks burning diesel fuel and more rail terminals using electricity."