I want my .ejs files to have html syntax, however, it always opens the files as Plain Text.
In sublime you can choose \"Open all with current extension as...\" then ch
For individual files you can use the Grammar Selector; Ctrl+Shift+L to set which language you're using on that file. Not the same as auto-detect but useful for those times when you're using a file that you don't want to set a default for.