(I'm going to answer this question primarily from the point of view of the wood, not the actual trees, as that's more interesting to me.)
I'm not aware of any systematic study done to identify the specific species of maple found in archaeological finds, but the two species mentioned by Roger B. Ulrich in Roman Woodworking, which is a book well worth your time, are Acer campestre (field maple) and Acer pseudoplatanus (sycamore maple), both of which were and are common throughout Italy and continental Europe in general. The former is the most common but has a relatively short trunk; as the hardest European maple, this is surely the maple used for writing tablets, and Ulrich suggests it was "probably" favoured for tool handles. The latter is the tallest of the European maples, and grows well in high, cool locations like the Apennines.
The most informative passage on maple in the classical corpus is in Pliny the Elder's Naturalis Historiae, 16.66 et seqq.:
Acer eiusdem fere amplitudinis, operum elegantia ac subtilitate citro secundum. Plura eius genera: album, quod praecipui candoris, vocatur Gallicum in transpadana Italia transque Alpes nascens. Alterum genus crispo macularum discursu, qui cum excellentior fuit, a similitudine caudae pavonum nomen accepit, in Histria Raetiaque praecipuum; e viliore genere crassivenium vocatur. Graeci situ discernunt, campestre enim candidum esse nec crispum—quod glinon vocant—montanum vero crispius duriusque, etiamnunc e mascula crispius ad lautiora opera, tertium genus zygian rubentem, fissili ligno, cortice livido, scabro. Hoc alii generis proprii esse malunt et Latine carpinum appellant.
My translation (comments in square brackets):
The maple, of roughly the same size [as the lime, the subject of the previous passage], is second to the citrus in elegance and subtlety for works. There are several kinds: white, which is of exceptional whiteness, is called Gallic and grows on the far side of the Po in Italy and on the far side of the Alps. The other kind has spots running in wavy lines, which, as it is especially good, due to its resemblance to a peacock's tail receives that name, and grows in Histria and Raetia; a baser kind is called thick-veined. The Greeks distinguish by location, holding that of the field to be white but not wavy—which they call glinos [?]—and that of the mountains truly wavy and hard, that of the male being harder still for more elegant works, a third type red zygia [ζυγία 'field maple'], with splittable wood, pale bark, rough. Others prefer to call this a distinct type and call it carpinus [typically hornbeam, not a maple] in Latin.
As you can see, Pliny mentions a distinction between "field" and "mountain" maple that could well correspond to the distinction between modern field maple and sycamore maple, but there's not really a good reason to exclude e.g. Acer platanoides (Norway maple), another maple endemic to Italy, from the conversation, and ultimately that distinction probably wouldn't have made much sense to a Roman, for whom the properties of the wood, which vary relatively little between many maple species, are primary: as far as Pliny is concerned, the important split is between plain "white" maple on the one hand and figured maple on the other. By acer pavonum 'maple of peacocks' he certainly means what today is usually called bird's-eye maple, which isn't a species but a poorly understood condition that can occur in many different maples. Likewise, what he calls crassivenius 'thick-veined' may be spalted maple or even wormy maple, which are also conditions rather than species—the former caused by fungus, the latter by beetle infestation.
As for the grammatical point, it seems like the plurals of acer are not actually attested (or I can't find them), but the stem is certainly ăcer-, not ăcr- or ācr-, and as a neuter 3rd-declension noun the nom. pl. would be acera.
(Apparently Pokorny does relate ăcer to ācer, suggesting the former was derived from the latter on account of the maple's pointy leaves, but few people seem to agree now. Most everyone agrees ācer is Indo-European, but for ăcer, the hard-to-square forms of the seemingly related OHG ahorn (< PGmc *aχurna-?), NHG Acher (< PGmc *aχira-?), and Gk. ἄκαστος 'maple' (< *ἄκαρ-στος?), ἄκαρνα 'laurel-tree' (both only Hesychian glosses) suggest late separate borrowings from some other language.)
