Taoiseach Leo Varadkar has said the border between Canada and the US is a hard border and would not be desirable on the island of Ireland.

Mr Varadkar visited the Queenstown-Lewistown border crossing today on a fact-finding exercise after some pro-Brexit politicians and commentators in the UK suggested the Canadian-US frontier was an example of a soft border that could work in Ireland.

Mr Varadkar said there were armed guards, dogs and checkpoints and extensive use of technology.

He said border officials told him it can be tough for small businesses working each side of the border to deal with customs requirements and tradesmen who work on both sides must go through a validation process each time they cross.

The Canadian Border Service operates 250 crossings and costs in excess of €1bn to operate annually.

Mr Varadkar said: "It was very interesting to get a detailed briefing from the Canadian Border Service - they have been working to streamline the border crossings for years but it is still a highly complex operation.

"And it costs a lot of money - the operational budget for the Canadian Border Agency is about one billion dollars to operate about 250 crossings.

"They have a system for what they call 'trusted importers' which is a three-stage process; providing advance information, risk assessment and processing at point of entry."

Mr Varadkar added: "They are also different standards for agriculture-food goods between the US and Canada and that can pose its own problems.

"It was a very interesting visit but it certainly left me in little doubt that the US-Canada model would not be desirable on the island of Ireland."

Earlier, Mr Varadkar said there is a need for more clarity from the British government about its intentions surrounding the customs union and single market post-Brexit.

Mr Varadkar said the British government has indicated it want to leave both, but in recently-published position papers it appears to want to keep the benefits of the customs union and single market. 

He said the two positions do not tally.

His comments come after Northern Ireland Secretary James Brokenshire insisted there is no possibility of the UK remaining within a customs union post-Brexit.

Mr Brokenshire, who is in Dublin for a series of meetings, said that to do so would prevent the UK from negotiating international trade deals.

However, he told businesses across the island of Ireland that there would be a period of implementation where the UK would adhere closely to the existing customs union.

Mr Brokenshire also addressed members of the British Irish Chamber of Commerce and will have discussions with Tánaiste Frances Fitzgerald and Minister for Justice Charlie Flanagan.

Speaking following a meeting with the Irish and British Chamber of Commerce, Mr Brokenshire said businesses had voiced their "desire for certainty, not wanting to see cliff edges, sudden shifts."

"We think it is important there is an implementation period where the UK would adhere closely to the existing customs union," said Mr Brokenshire.

"But ultimately it is about the UK being able to negotiate international trade deals. We want to harness those freedoms. If we were to remain in the customs union that would prevent us from doing so.

"We are leaving the EU, customs union and single market. We have set out options as to how we can achieve that frictionless trade," he added.

Mr Brokenshire said he had also reassured business leaders during the meeting of the UK's intent to ensure there will be no return to a hard border across the island of Ireland."

He has also scheduled meetings in Dublin with Government ministers including Minister for Justice Charlie Flanagan, Tánaiste Frances Fitzgerald and Minister for Foreign Affairs Simon Coveney.

The Director General of the British Irish Chamber of Commerce described the meeting with Mr Brokenshire as an important one.

John McGrane told RTÉ's News at One that constructive ideas are beginning to emerge, grounded in the idea of a form of a customs union that could lead to a borderless trade situation between north and south. 

Mr McGrane said he believes what is on the table, at this time, is the concept of a customs union membership for the whole of the UK that is different to today's customs union.

Analysis from RTÉ's Northern Editor

One reason for James Brokenshire's visit is to compare notes with Simon Coveney about the chances of restoring power-sharing. 

They may decide, as a next step, to take further soundings with Northern Ireland's main political parties.

But Brexit-related business is a significant component of this visit.

Brokenshire is trusted by Theresa May.

He used to work directly to her when she was Home Secretary. He is also seen as a safe pair of hands, unlikely to make controversial comments. 

One purpose of today's activities may involve assessing the mood in Dublin, following the publication of two Brexit papers by the British government last week. 

The UK is due to leave the EU in March 2019. 

But in October, EU leaders will decide if sufficient progress has been made on three issues, including Ireland-related matters.

That's an important date because after it some of Ireland's negotiating space and importance may diminish.