The pipeline may create some jobs, but they will be temporary. These pipelines are meant to basically run by themselves. So we may create a few thousand temporary construction jobs, but TransCanada - who would own and operate the pipeline - have said numerous times that the pipeline would only create a few hundred permanent jobs in the United States. TransCanada itself has issued a report saying the highest potential number of temporary jobs the project would create is just under 5,000. Talk about a drop in the bucket.
And as for reducing oil prices, the majority of the oil would be exported from Houston/Galveston/Port Arthur, Texas to markets in Central and South America and would thus have little impact on domestic gas prices. Additionally, these ports are designated Foreign Trade Zones, so we couldn't even tax the exports.