If you want to submit your paper to Elsevier (and this is the only good reason to use
elsarticle.cls, I believe) you should follow their instructions as much as possible, use their template as-is and should definitely not modify it to use a package that is incompatible with the defaults loaded by the class (for
elsarticle that would be
Publisher classes are usually meant to enable a simple and smooth workflow for the publisher. The workflow for citations and the bibliography with
biblatex is significantly different from the workflow with BibTeX. For starters
biblatex does not produce typesettable TeX code in a
thebibliography environment. That means that publishers, whose workflow uses
thebibliography as produced by BibTeX or used in manual bibliographies, will in all likeliness not be able to process submissions with
biblatex bibliographies properly. See also Biblatex: submitting to a journal.
It is possible to make
biblatex (see biblatex instead of natbib in elsarticle, how?), but I'm almost certain that Elsevier won't like that (cf. for example I cannot make my biblatex work). If you need something in your paper that the provided template can't do and that can't be implemented in a compatible way, you should contact the editor and ask for further instructions.