Suetonius says in Julius Caesar, 19,2
'Igitur cum Bibulo consul creatur. Eandem ob causam opera ab optimatibus data est, ut provinciae futuris consulibus minimi negotii, id est silvae callesque, decernerentur'
in the Loeb edition translated thus:
"So Caesar was chosen consul with Bibulus. With the same motives the aristocracy took care that provinces of the smallest importance should be assigned to the newly elected consuls; that is, mere woods and pastures.15 "
note 15: "If silvae callesque should stand in the text, it is used in a different sense from calles in Tac. Ann. 4.27. It seems to designate provinces where the duties of the governor would be confined to guarding the mountain-pastures and keeping the woods free from brigands. The senate would not run the risk of letting Caesar secure a province involving the command of an army."
The problem is that according to the Lex Sempronia de provinciis consularibus the proconsular provinces, ie those the consuls were given to rule the year following the year of their consulship, should be assigned *before* the consuls were elected. This means that the senate could not have had the intention Suetonius 169 years later impugns to them since the senators wouldn't know who would be elected consuls. The relevant passage I would rather translate as:
"So Caesar was chosen consul with Bibulus. With the same motives the aristocracy *had taken* care that provinces of the smallest importance should be assigned to the *future* consuls; that is, mere woods and pastures." Apparently Suetonius surmises that by that time it was obvious to everyone and the senate that Caesar would become elected.
It seems more likely to me that what the senate assigned to the future consuls, that which Suetonius calls 'silvae callesque' but which was in fact the two provinces of Gallia Cisalpina and Illyricum, which would have been seen by Suetonius as irrelevant to Caesar's future course as the conqueror of Gaul, and that what they actually did assign to the future consuls was that task which Pompey's man Afranius that same year had been carrying out either in the Alps north of Aquileia, or in Illyricum, for which he was awarded a triumph, and the three legions he had carried them out with. The Lex Vatinia, on the other hand (carried not by the senate, but by popular assembly) was then solely about the length of his imperium there (five years), not about the assignation of those proconsular provinces, which would have been illegal under the Lex Sempronia.
The relevance of this is that at least the year before (61 BCE) there must have been awareness in Rome of something large coming that way, which deserved that much attention. The reason why this is never found in the sources, one might guess, might be found here: