The scheme could allow the 175-mile journey between the Butt of Lewis and Vatersay to be completed without the need for a ferry.
Although plans are in the early stages, bridges could be built over the Sound of Harris and the Sound of Barra, according to reports.
Ian Fordham, chairman of Outer Hebrides Tourism, told The Herald newspaper the scheme would be an “investment for the future” and save the need to introduce more island ferry services.
He said: “We know that the Sound of Harris ferry is always a bottleneck. The ferry is pretty much fully booked all the way through summer. This would really enhance the visitor experience.”
The scheme is one of 11 priority projects listed by Western Isles Council as part of a proposed “Islands Deal” investment which is being considered by the UK and Scottish governments.
Western Isles, Shetland and Orkney are working together to develop a funding bid that will significantly boost the economy of the islands.
New road connections over the Sound of Harris and the Sound of Barra have been outlined, connecting Harris to North Uist and South Uist to Barra.
Other projects put forward byt Western Isles Council include a regeneration scheme in Stornoway and the UK’s first designated spaceport, The Herald said.
Mr Fordham said fixed links between the islands had been “on the agenda for a while” but had always come with a large price-tag attached.
Earlier plans for a 15-mile tunnel between North Uist and Skye - connecting the Outer Hebrides to the mainland - had “dropped out as a priority, he added.
A Scottish Government spokeswoman said: “We are committed to working with Comhairle nan Eilean Siar [Western Isles Council], Orkney Islands Council and Shetland Island Council on an Islands Deal, and looks forward to receiving the detailed proposals the three island local authorities have been working on in the coming months.”