In what ways are Wyatt's "Whoso List to Hunt", Howard's "Love That Doth" and Sidney's Astrophil and Stella similar and different from each other?
This is a very broad question considering that Astrophil and Stella is a sonnet cycle comprised of 108 sonnets and songs of other lyric types, while "Whoso List" and "Love that Lost" are both individual sonnets. Therein is a significant difference between Wyatt's, Howard's, and Sidney's works: two are individual sonnets, the other is a complete sonnet cycle that tracks the developments of a whole romance from inspiration to rejection: "tracks in linked sonnets the progressive rise and fall of a love relationship" (Sanders, Goucher College). This emphasizes the difference that while Wyatt and Howard use variations of Petrarch's sonnet form, Sidney uses sonnet forms and other lyric forms in his cycle. As Art Sanders of Goucher college says, Sidney is given to experimentation and displays some of his experimental forms in the Astrophil cycle.
typically for Sidney who was an avid experimenter in poetic forms, the 108 sonnets are interrupted by 11 songs of varying forms... (Art Sanders, Ph.D., Goucher College)
As for the sonnets specifically, Wyatt's is structured as a Petrarchan octet (8 lines) followed by a sestet (6 lines) with one volta (change or "turn" in subjects within the overall topic) between lines 8 and 9 (or at line 9). Wyatt varies the Petrarchan form, which never had ending rhyming lines in a couplet, by ending "Whoso List" with a couplet (defined as two rhyming lines). Wyatt's rhyme scheme therefore is abbaabba cddcee with concatenation (linking of subjects through internal couplets) at the aa rhyme at lines 4 and 5.
Howard's is structured in the form of what would later be called the Shakespearean sonnet (though not developed by, only popularized by, Shakespeare). It has three quatrains and an ending couplet (which by definition rhymes). The third quatrain borrows the c rhyme from the second quatrain thereby connecting the subjects of "pain" in both quatrains. This form allows for two voltas where the subject on the topic changes. Here the change is from the subject of "he" to that of "she," then again from "she" to personified "coward love." Howard's rhyme scheme is abab cdcd ecec ff.
As an additional note, while voltas separate and change subjects, concatenation (internal couplet linking) continues the subject from one quatrain to the next: one separates subjects, one continues the same subject.
I am of them that farthest cometh behind. - a
Yet may I by no means my wearied mind - a
(Wyatt, "Whoso List to Hunt")
But she that taught me love and suffer pain, - c
For my lord's guilt thus faultless bide I pain; - c
(Howard, "Love that Doth Reign and Live")