Both of these long poems are “journey” literature. That is, the metaphor of life as a journey underlies each, even though the characters are on a physical or spiritual journey as well.
A major similarity is that the two authors are both using the poem as an opportunity to draw portraits of real people, but sufficiently disguised and fictionalized to avoid social or religious repercussions. Dante inserts many portraits of past and present sinners in his Hell, and Chaucer parodies the hypocrisies of his era in the persons going on the pilgrimage to Canterbury. The technique, termed “roman a clef” when it reaches modern times in novel form, allows satirical comment without legal repercussions to the writer.
Another important similarity is the episodic nature of the narratives. That is, the larger story is told by chaining together many small anecdotes.
Finally, the comparison most valuable from a literary standpoint is that both poems contributed to the growth, refinement, and acceptance of their languages (Italian and English).
There are many differences between them also, of course, the most important being the seriousness of the religious tone (Dante was serious; Chaucer was almost mocking).