Allusion #9 - Juno's swans

As You Like It Act 1 Scene 3

CELIA  ... (this part removed)
        Why so am I. We still have slept together,
        Rose at an instant, learned, played, eat together,
        And, wheresoe'er we went, like Juno’s swans
        Still we went coupled and inseparable.

In this quote, "we" means Celia and Rosalind. Although it was Venus who had swans pulling her chariot (Shakespeare must have been confused), these two swans were nevertheless always together.  Rosalind and Celia are a lot like this; they are always found with each other. Together, they watch the wrestling match, meet Orlando, escape to the Forest of Arden, see Silvius' declaration of love, read Orlando's love poems, spy on Phoebe and Silvius, hear Jacques' explanation of the cause of his melancholy, test Orlando's love for Rosalind, hear the heroic story of Orlando told by Oliver, and so on and so forth.Carefully looking through the book will show that, except for Act 5 Scene 2, all scenes containing Rosalind also contain Celia, and vice versa. This proves that Celia and Rosalind are always united.
Venus'/Juno's swans also loved each other; this is shown between the two girls in As You Like It when it is mentioned that Duke Frederick kept Rosalind at court only for Celia's sake.
These two swans were also loyal to each other. The same can be said for Rosalind and Celia. When Duke Frederick banishes Rosalind from the court, Celia abandons her title, father, and belongings to stay with Rosalind. 
All in all, when Celia alludes to Juno's (or Venus') swans, she is describing the deepness of her love and loyalty to Rosalind.