They both lived on Prince Edward Island.
They were both dreamers with imagination.
They were both orphans who were taken in by strict spinsters (though I think Marilla is a bit mellower than Aunt Elizabeth).
They both wrote poetry and short stories.
They both give names to objects, places, etc.
Emily's "the flash" is equal to Anne's "thrill."
Emily has Mr. Francis Carpenter to encourage her writing; Anne has Miss Muriel Stacy to encourage her ambitions.
They were both subject to dares (Emily was dared to sleep in the garret, and saved the house from burning down; Anne was dared to walk the ridgepole of a roof and broke her ankle).
They both went to college (Emily at Shrewsbury and Anne at Redmond).
Their best friends both got drunk (Ilse Burnley on the night of a storm and Diana Barry during Anne's tea party).
They were both asked to write an obituary (Emily refused outright, Anne agreed to do so but regretted it later when her work was altered without her consent).