Facebook Inc. announced Wednesday that its Messenger app is being opened up as a platform for other other apps, and at least two Canadian companies have signed on to provide their services. “Messenger Platform brings even more ways for the 600 million people who use Messenger every month to express themselves,” Facebook said in a release. “With more than 40 new apps, people can enhance their conversations with GIFs, photos, videos, audio clips and more.” Toronto-based Keek Inc. said in a release it is launching a separate app called Keek for Messenger that will...